1. Field of the Invention
The present invention relates to a laser diode pumped solid-state laser apparatus which has a laser medium and a non-linear optical element in a resonator, for emitting fundamental-wave oscillated light and non-linear light from the laser medium excited by a semiconductor laser.
2. Description of the Related Art
A solid-state laser apparatus is known which uses a semiconductor laser composed of GaAlAs or the like for exciting a laser medium such as Nd:YAG crystal provided in a resonator to generate a laser light.
For generation of shorter wave-length laser light, numerous types of solid-state laser apparatuses have been proposed which have substantially a laser medium and a non-linear optical crystal provided in a common resonator to convert an oscillated light output of the laser medium to a non-linear light such as a second harmonic (for example, as disclosed in Japanese Unexamined Patent Publications JP-A 4-283977 (1992) and JP-A 6-69567 (1994), and Japanese Unexamined Utility Model JP-U 4-07375 (1992)). When the laser medium is YAG crystal and the non-linear optical crystal is titanium potassium phosphate KTiOPO.sub.4 (abbreviated to KTP), the oscillated light from the YAG crystal can be converted from its original wavelength of 1064 nm to a half of 532 nm of green light wavelength.
It is however needed for such a donventional solid-state laser apparatus to position the semiconductor laser, laser medium, and non-linear optical element at high accuracy. When the optical axes of pumping light, oscillated light, and non-linear light fail to be aligned on the order of micrometers, the efficiency of light conversion will be remarkably declined.
Also, an adverse change in the distance between the optical components or the optical device and its holding member due to thermal expansion may result in decreases of conversion efficiency due to displacement of the optical axis or fluctuations of output due to mode hopping.